In theory, Google Takeout lets you download all the data Google stores for you (or about you). Among these there should be the backup content of my Android devices.
Is it Android Backup included in the Takeout?
Should it be?
Is there a way to request that?
From https://takeout.google.com, you can download files stored in My Drive and Computers, which don't include mobile Backups:
From the question: Downloading Phone's Backups from Google Drive to PC or Alternative Phone:
You can not download the backup onto your PC. It can only be installed back onto the product it came from, or if it is an iOS or Android backup, then that can only go back onto that operating system (so back onto another phone or the same phone).
However you can "View details about a backup" and "Delete a backup" directly from a web browser or Google Drive app (source: Manage & restore your mobile backups in Google Drive).
Q & A